The subject of auto reversing is a topic unto itself. Guess that
will be something for a column in the near future.
One rail or two?
Relay-designed circuit breakers tended to disconnect the pow-
er from both rails. Electronic breakers tend to only open one
rail. In normal usage, the difference is very minimal. There is
one circumstance where there can be an issue with only one
rail opening.
Consider a modular meet where two adjoining (sets of) mod-
ules are wired differently, one interrupting the outside rail and
the other interrupting the inside rail. It is possible to have a
short on the boundary between these two (sets of) modules
that will not shut down the districts, but will take down the
booster(s) supplying them.
There are two ways to remedy this.
Set a standard that a specific rail is interrupted and en-
force it.
Use a circuit breaker that interrupts both rails.
If I were setting standards for a modular club, I’d include a re-
quirement that each section (group of modules that must be
used together) drive a local DCC bus off the main DCC bus that
passes through the module (set). This local bus would be iso-
lated from the DCC bus with a circuit breaker that interrupts
the outside rail. Thus every scene becomes its own domain and
a short within it won’t bring down the entire setup.
I asked Larry Maier, the designer of the PSx series about this.
His reply: “The PSX breaker only opens one rail because we
know that model railroaders have a limited budget and we are
trying to make them as cost effective and affordable as pos-
sible. To answer your question: Yes, the PSX-AR opens both
DCC Impulses Column - 9
MRH-Nov 2014
